JPH11226712A - Mold powder for casting high al-containing steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide mold powder for casting a high Al-containing steel, that the change of this composition with the lapse of time is not generated over the process of continuous casting of the high Al-containing molten steel and which has the necessary various characteristics as the powder for the continuous casting and from which a cast slab having no defect can be produced. SOLUTION: The composition of the mold powder for casting the high Al- containing steel is composed, by weight, of 1.0-5.0% T.C, 15-30% SiO2 10-25% Al2 O3 , 15-30% CaO, 10-25% Na2 O, 10-15% F, 0-5% Li2 O, 3-10% BaO and the balance inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting mold powder used for continuous casting of steel, and particularly to a continuous casting of a high Al content steel containing a large amount of Al, which suppresses a change in composition of a molten powder due to Al in the steel. The present invention relates to a mold powder for casting a high Al content steel capable of obtaining a slab having excellent surface properties.

[0002]

2. Description of the Related Art In continuous casting of steel, a mold powder is used for lubrication between a mold and a slab, and the operation is performed while the molten powder is made to flow between the mold and the slab. Therefore, it is preferable that the composition of this mold powder is adjusted so as to obtain appropriate melting characteristics with CaO and SiO ₂ as main components, and that the composition and the melting characteristics are maintained during the process of continuous casting.

However, when continuously casting a high Al content steel containing as much as 0.1% or more of Al, the following reaction in which the SiO ₂ content in the mold powder is reduced by Al in the steel, 3 (SiO ₂ ) +4 [Al] = 3 [Si] +2 (Al ₂ O ₃ ) occurs, SiO ₂ in the molten mold powder decreases, and Al ₂ O ₃ increases. FIG. 3 shows the change over time of the composition of a conventional molten mold powder when a high Al content steel having the composition shown in Table 1 is continuously cast, and FIG. 4 shows the change over time of the viscosity generated correspondingly. However, after the start of continuous casting, the content of Al ₂ O ₃ increases while the content of SiO ₂ in the molten powder gradually decreases, and as a result, the basicity (CaO 2
/ SiO ₂ ) and the viscosity increases.

[0004]

[Table 1]

When such a phenomenon occurs, the gelenite phase (2CaO.Al) is added to the molten mold powder.
₂ O ₃ · SiO ₂ ) is precipitated, so that the inflow of the molten powder is not carried out smoothly, and various defects occur in the slab,
There is a problem that the slab must be maintained.
Such a high-Al-containing steel means for solving the continuous casting problems of, for example, in JP-A-63-10052 to reduce the CaO / SiO ₂ powder itself with 0.5 to 0.8, SiO ₂ decreases Proposals have been made to reduce the effects of this. Japanese Patent Application Laid-Open No. 9-76049 proposes a composition in which Al ₂ O ₃ is added in an amount of about 20% in advance so as to be less susceptible to a composition change due to Al in steel.

[0006]

However, in the proposal disclosed in Japanese Patent Application Laid-Open No. 63-10052, it is essentially unavoidable that SiO ₂ is reduced during casting, and the components change over time during casting. Some problems remain. On the other hand, in the proposal disclosed in Japanese Patent Application Laid-Open No. 9-76049, although the composition variation due to the reduction action of Al is reduced to some extent, the composition variation is likely to occur immediately after the start of casting, and the viscosity becomes higher than the initial value. As a result, there has been a problem that the surface of the slab must be cleaned.

The present invention has been made to solve the above-mentioned problems of the prior art, and does not cause a change in composition over time during the continuous casting process of a high Al content molten steel, and also provides various necessary powders for continuous casting. An object of the present invention is to provide a mold powder for casting a high-Al-content steel that has characteristics and can produce a slab without defects.

[0008]

Means for Solving the Problems The present inventors have proposed a conventional mold powder for a high Al content steel, particularly, Japanese Patent Application Laid-Open No. 9-7 / 1997.
The problem of the proposal disclosed in Japanese Patent No. 6049 was investigated, and it was first assumed that the basic component was close to the attained composition at the time of using the normal mold powder, and that the composition no longer substantially changed. It was confirmed that the reason was that the flux component was inadequate, and the present invention was completed as a composition mixture for improving this.

More specifically, the present invention relates to a composition of a mold powder for casting containing high Al steel, which has a T.V. C: 1.0-
_{5.0%, SiO 2: 15~30%} , Al 2 O 3: 10~
25%, CaO: 15~30%, Na 2 O: 10~25
%, F: 10~15%, Li 2 O: 0~5%, BaO:
3 to 10%, with the balance being unavoidable impurities.

Further, the present invention provides the above-mentioned mold powder having a basicity, that is, CaO / SiO ₂ of 0.9 to 1.
1. The melting point is 900 to 1200 ° C, and the viscosity at 1300 ° C is 1.5 P or more.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The mold powder of the present invention will be specifically described below, including the effects of the powder constituents. T. C, that is, the total amount of carbon has a function of controlling the melting rate as a powder aggregate.
If this amount is less than 1%, the melting rate will be too fast, while if it exceeds 5.0%, the melting rate will be too fast and the inflow of the molten powder will be too large.

Al ₂ O ₃ , SiO ₂ , and CaO are the basic components of the mold powder, and these are assumed to be close to the final composition when used. The final attained composition is determined empirically, and as shown in FIG. 3, a normal mold powder may be used, and the composition of the molten powder may be a certain time after the start of casting, for example, 30 minutes after the start of casting. .
Specifically, SiO ₂ : 15 to 30%, Al ₂ O ₃ : 10
25%, CaO: 15-30%. Within this range, there is substantially no effect of the reduction of SiO ₂ by Al in the steel.

The flux component is added for adjusting the melting point and viscosity of the powder. Especially with BaO as a flux component in the present invention, by suppressing the precipitation of gehlenite crystals in SiO ₂ -Al ₂ O ₃ -CaO based ternary phase diagram,
Reduce melting point and viscosity. Therefore, the addition amount of BaO is set to 3 to 10%. Other flux components, Na ₂ O,
F and Li ₂ O are added so as to obtain the necessary melting point and viscosity in consideration of the relationship with the above basic components. Specifically, the amount is 10 to 25% of Na ₂ O, 10 to 15% of F, L
i ₂ O may be in the range of 0 to 5%.

If the basic component and the flux component are blended as described above, the operation can be performed in a state where the physical properties such as the powder composition and the viscosity are stable during the continuous casting, but the melting point is further increased to 900 to 1200 ° C. If the viscosity at 1300 ° C. is reduced to 1.5 P (poise) or less, the effect of the present invention can be further ensured.

FIG. 1 shows the change over time of the composition of the molten powder when the high Al content steel shown in Table 1 is cast using the mold powder of the present invention, and FIG. 2 shows the change of the viscosity characteristics according to the change. . Since the powder of the present invention has almost the same composition as the composition in which the composition variation in FIG. 3 is saturated, there was almost no change in the composition of the molten powder during casting. As a result, in continuous casting of high Al steel content steel, there was no problem in the surface properties, care was substantially unnecessary, and casting without a decrease in casting speed could be achieved.

[0016]

According to the present invention, it is possible to suppress the composition fluctuation of the molten powder in the mold at the time of continuous casting of high Al content steel, and to maintain the physical properties such as the viscosity and the melting point almost constant from the beginning to the end of casting. Therefore, it was possible to cast a slab with good surface cleanness without lowering the casting speed.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the elapsed time after the start of casting and the composition of molten powder when high Al steel is cast using the mold powder of the present invention.

FIG. 2 is a graph showing the relationship between the elapsed time after the start of casting and the viscosity of the molten powder, which correspond to the change in the composition of the molten powder shown in FIG.

FIG. 3 is a diagram showing the relationship between the elapsed time after the start of casting and the composition of molten powder when high Al steel is cast using conventional mold powder.

FIG. 4 is a graph showing the relationship between the elapsed time after the start of casting and the viscosity of the molten powder, corresponding to the change in the composition of the molten powder shown in FIG.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takeshi Ken Asahina 1-chome, Mizushima Kawasaki-dori, Kurashiki-shi, Okayama Pref. 1-chome (without address) Inside Mizushima Steel Works, Kawasaki Steel Corporation

Claims (2)

[Claims] 1. The T.C. C: 1.0 to 5.0%, S
_{iO 2: 15~30%, Al 2} O 3: 10~25%, Ca
_{O: 15~30%, Na 2 O} : 10~25%, F: 10
１５15%, Li ₂ O: 0 to 5%, BaO: 3 to 10%,
A mold powder for casting containing high Al steel, characterized in that the remainder comprises inevitable impurities. 2. CaO / SiO ₂ : 0.9-1.1, melting point: 900-1200 ° C., viscosity at 1300 ° C .: 1.5
The mold powder for casting a high Al content steel according to claim 1, wherein the mold powder is P or more.